Alright, well so far it seems as though the only cheap way of making a DIY furnace is to use microwave radiation.
What I learned from research and the video are that...

-glass melts in the microwave after being torched
-microwave radiation works on WATER MOLECULES in the microwaved material
-plasma sparks can be a problem

One of the biggest concepts here is that adding water to the glass will make this idea FAR more effective.

I'm thinking that you could take out the microwave's radio device and then make a larger inside cooking area for it so that the plasma sparks can't reach the inner walls, maybe even with stronger walls and such so that plasma sparks cannot damage them, and glass can just melt at the bottom I bet, as long as the door doesn't reach down to the bottom of it, then this can be totally possible. The only thing that might go wrong is that with a larger inside to the microwave, a larger corresponding amount of radiation may be required. I've read that a microwave operating while opened has no effect on lab rats in the same room, as for the plasma, IDK anything about that, but I'd just say stay back lol. Maybe the radiation emitting device in a microwave can be taken out and used in open air near the glass?

I got my information from some guy on Yahoo here lol seems legit doe "http://answers.yahoo.com/question/in...0212330AAGTBsZ"

Another idea for larger scale:
I'm wondering if a DIY microwave can be made, so that more powerful radioactivity can be produced (can't be expensive, I'd imagine), and this could be put into a larger space closed area (I guess walled with whatever a normal microwave is walled with inside) so that the plasma sparks would have too much distance to travel before they reached the device's inner walls to damage it.